Attention has been focused on the technology of utilizing LEDs (Light Emitting Diodes) as a light source of a projector for projecting images onto a screen, such as a liquid-crystal projector and a DMD (Digital Micromirror Device) projector (see Patent Document 1).
Projectors, which have LEDs as a light source, offer the advantage of a longer operating life and a higher reliability due to a longer operating life and a higher reliability of LEDs.
However, since lights from LEDs have low brightness as lights for projectors, it is not easy to obtain images with ample brightness in projectors having LEDs as a light source. The amount of lights from the light source that can be utilized by a display panel as a projection light, is limited by the etendue. Specifically, if the product of the light-emitting area and a radiation angle of the light source is not made equal to or smaller than the product of the area of an incidence plane of the display panel and an incident angle that is determined by a F number of an illumination optical system, then the light from the light source can not be efficiently utilized as a projection light.
For a light source using LEDs, if the light-emitting area is increased, the amount of light can be increased, but the etendues of the light source becomes larger. From the limitation of etendues, for a light source of a projector, it is desired to increase the amount of light without increasing the light-emitting area. However, for a light source using LEDs, it is difficult to increase the amount of light without increasing the light-emitting area.